The homopolymerisation of .alpha.-olefins and the copolymerisation of .alpha.-olefins with one another in the presence of Ziegler-Natta catalysts are known. Although the properties which are due to the olefinic character of these polymers, such as resistance to water and chemical resistance to acids and alkalis, are generally advantageous, the absence of polar groups gives rise to certain disadvantages, such as poor dyeability, weak adhesion, poor printability and poor miscibility with other polymers, particularly polymers containing polar groups. Pure polyolefins become electrostatically charged more easily and attract dust and dirt particles.
It is known that copolymers of olefins and unsaturated monomers containing polar groups can be produced by radical polymerisation but crystalline copolymers cannot be obtained by this process if olefins containing more than 2 carbon atoms are used. In addition, it is not possible to obtain a sufficiently high degree of polymerisation when radical copolymerisation is carried out with higher olefins.
The copolymerisation of .alpha.-olefins with .alpha.-olefins containing polar groups in the presence of Ziegler-Natta catalysts is also known in principle, but the activity of the catalysts is generally reduced to a considerable extent.
Examples of processes for the copolymerisation of .alpha.-olefins with ethylenically unsaturated monomers containing polar groups can be found in J. Polym. Sci., Part A-1, 9, 471 to 483 (1971), in German Offenlegungsschrift No. 1,947,109 and also in British Pat. No. 1,505,480.
Thus, propylene/acrylic acid copolymers can be obtained by copolymerising propylene and the compound ##STR9## in the presence of a catalyst comprising TiCl.sub.3 /diethyl aluminium chloride. Copolymers obtained in this way are 54% soluble in boiling concentrated hydrochloric acid and can only be produced in a specific yield of from about 30 to 50 g of polymer per g of Ti.h.atm.
The process described in German Offenlegungsschrift No. 1,947,109 gives copolymers of .alpha.-olefin units and units corresponding to the formula ##STR10## wherein Z represents a difunctional methylene group, n is .gtoreq.2 and A' is a hydrogen atom or an acyl group. In this process, the polar comonomer is used in the form of a metal compound corresponding to the following formula EQU (CH.sub.2 =CH--Z--O).sub.n MA.sub.m
wherein Z represents a difunctional hydrocarbon group containing from 2 to 15 carbon atoms, A represents a halogen atom and/or a monofunctional hydrocarbon group, M represents a metal from Groups I to IV of the Periodic Table and n and m are integers so that the sum of n+m corresponds to the valency of the metal. The catalyst used is a halogen compound of titanium or vanadium whilst the co-catalyst is either the metal compound (CH.sub.2 =C--Z--O).sub.n MA.sub.m, if it contains alkyl groups, or else aluminium or zinc alkyls are added.
The specific yields of copolymers as measured in g of polymer/g Ti.h.atm. (propylene) amount to between 10 and 70.
The process for synthesising copolymers described in British Patent No. 1,505,480 is a two-stage process which gives block-like copolymers having the following structure; EQU [poly-.alpha.-olefin]-[polyvinyl compound].
In a first stage, an .alpha.-olefin is polymerised in known manner using Ziegler-Natta catalysts. In a second stage, the vinyl compound, preferably an acrylate or a methacrylate, is added to the still active polyolefin ends in the simultaneous presence of phosphines and halogenated hydrocarbons as co-components.
By this method, it is possible with ethylene as the olefin component to obtain copolymers containing from 30 to 40% of methyl methacrylate for a homopolymer content of the methyl methacrylate of around 5%. With propylene as the olefin component, the copolymer contains approximately 0.5% by weight of methyl methacrylate, of which 2.6% by weight is in the form of homopolymer, for a specific yield of approximately 10 to 30 g of polymer/g T.h.atm.